In recent years, in order to improve tire forming accuracy, a tire forming method utilizing a rigid core (hereinafter, called “core method”) has been proposed. (cf. Patent documents 1, 2 for example)
The rigid core has an outer shape which substantially accord with the inner surface of the vulcanized tire.
On the outer surface of the rigid core, by applying tire construction members, an inner liner, a carcass ply, a belt ply, a sidewall rubber, a tread rubber and the like in series, a green tire is formed.
The green tire is put in a vulcanizing mold together with the rigid core, and the green tire is vulcanization-molded between the rigid core as an inner mold and the vulcanizing mold as an outer mold.
In the core method, after the completion of the vulcanization, the rigid core and the vulcanized tire which are combined into one are took out from the vulcanizing mold.
At that moment, the rigid core and the vulcanized tire are in a high-temperature state of 160 to 190 deg. C.
Accordingly, if the combined is left as it is (naturally-cooled), it takes much time to cool the rigid core down to a safe temperature (for example, about 50 deg. C.). Therefore, it takes much time to disassemble and remove the rigid core from the vulcanized tire to furnish it to another subsequent green tire forming process, and there is a problem of lowered production efficiency.
Further, if the combined is left as it is (naturally-cooled), there is a possibility that the vulcanized tire is over-vulcanized by the heat from the rigid core, and the quality of the tire is decreased.
In the vulcanization process, on the other hand, it is required to quickly heat up the rigid core to the vulcanization temperature in order to shorten the time for the vulcanization process and improve the production efficiency.
But, in the green tire forming process, the rigid core is in a lowered temperature state.
Therefore, if the heating is started after the rigid core is put in the mold, it takes long time to raise the temperature of the rigid core, and it becomes difficult to fully achieve the shortening of the time for the vulcanization process.
In the core method, as the rigid core is repeatedly used as explained above, the following is important in order to increase the production efficiency
(a) to cool the rigid core quickly as far as possible and remove it from the vulcanized tire after the vulcanization process, and furnish it to another subsequent green tire forming process,
(b) to raise the temperature of the rigid core quickly as far as possible in the vulcanization process, and shorten the time for the vulcanization process.